AGING LIVE ANTARCTIC FUR SEALS AND SOUTHERN ELEPHANT SEALS

This study describes a method for extracting post-canine or incisor teeth from live antarctic fur seals ( Arctocephalus gazella ) and southern elephant seals ( Mirounga leonina ) respectively and their use to determine age in a field situation. Dental elevators were used to loosen the teeth from the alveolus and periodental ligament. Most teeth were removed within l-2 min and a total of 214 and 81 teeth were collected by this method from antarctic fur seals and southern elephant seals respectively. No seal recaptured at intervals up to a year after a tooth was extracted showed signs of infection or distress related to removal of the tooth. Teeth were thin-sectioned for the purpose of aging. In both species cementum growth layer groups were a more satisfactory indicator of age than dentinal growth layer groups. Estimates of age from cementum growth layers were confirmed for Antarctic fur seals using seals which had been tagged as pups up to 16 yr before sampling.     

Laminae in the teeth of the Cape fur seal used for age determination

A sample of 40 known age Cape fur seal, $\text{Arctocephalus pusillus}$ canine teeth were histologically and manually sectioned and examined for laminae to determine if these growth layers could be used for age determination in this species of seal. Results of this investigation indicate that two laminae (one opaque and one translucent) are deposited per annum and that these structures provide an accurate method for aging seals 2 years old or less; agreement between age and laminae was also obtained for seals up to 8 years of age, but the small number (N = 3) of known-aged canines older than two years does not permit a definite conclusion as to the applicability of the method throughout the life span of the Cape fur seal.     

TOOTH WEIGHTS OF JUVENILE MALE NORTHERN FUR SEALS, CALLORHINUS URSINUS

Tooth weight and body length of juvenile male northern fur seals, Callorhinus ursinus , collected on St. Paul Island, Alaska, from 1948 to 1984 were compared. The relationship between these variables was investigated for individual and combined age classes. A density-dependent increase in mean tooth weight occurred during a decline in fur seal abundance. Consistent, though poorly understood, differences in tooth weight were found among males associated with different rookeries (breeding grounds). Storing the teeth for long periods may affect the weights, but such effects, if any, are too small to account for the changes observed.     

Analysis of growth and stable isotopes in teeth of male Australian fur seals reveals interannual variability in prey resources

To detect and monitor long‐term ecosystem responses to environmental variability, managers must utilize reliable and quantitative techniques to predict future ecosystem responses. Canine teeth from 67 male Australian fur seals (aged 2–19 yr), collected at Seal Rocks, between 1967 and 1976, were measured for relative growth within the dentine growth layer groups (GLGs), as an index of body growth. Fluctuations in relative growth were apparent during 1956–1971, suggesting interannual variation in prey resources within Bass Strait. These were positively correlated with the Southern Oscillation Index and negatively with the Indian Ocean Subtropical Dipole, both on a 2 yr lag. The observed delay may reflect the time required for the nutrient cascade to filter through to the predominantly benthic prey of Australian fur seals. Stable isotope analysis (δ¹⁵N/δ¹³C) was also used to investigate whether fluctuations in growth were associated with differences in diet. Relative growth was found to be negatively correlated with δ¹⁵N, suggesting years of greater resource availability may be associated with individuals consuming proportionally more prey biomass of lower isotopic value. This study demonstrates that fluctuations in the dentine GLGs of male Australian fur seals are related to environmental parameters, suggesting variation in body growth is mediated by changes in prey resources.     

Incremental growth layers in the dentine of dugong incisors (Dugong dugon (Müller)) and their application to age determination

An attempt has been made to determine the absoulte age, in terms of incremental growth layers in the dentine of unworn incisors, of dugong skulls already relatively aged by Mitchell (1973). About 60 loose incisors were also included in the study. Layer numbers were found to range from zeros to 57 1/2. Upper jaw tooth succession was related to layer number, tooth 5 coming into wear at 2 1/2 to 3 layers and tooth 6 between 5 1/2 and 8 1/2 layers. The date of death of the animals from which 11 of the skulls came was known with certainty and a twelfth possibly, and this information indicated that the layers are either annual or biannual but are unlikely to be laid down more frequently than this. It is suggested that sexual maturity is reached at approximately 10 layers (i.e. 10 or 5 years of age).     

Age-Related Changes in Functional Teeth in the Pacific Walrus (<Emphasis Type="Italic">Odobenus rosmarus divergens</Emphasis>)

We examined functional teeth (except for upper canine teeth) of Pacific walruses that died or were harvested on the coast of the Chukchi Peninsula in 2005, 2007–2008, and 2010–2011. The dynamics of deposition of annual cement layers was investigated. The rate of cement deposition on the walls of tooth roots decreased significantly with age. The rate of its deposition on the lingual side of the upper teeth was much higher than that on their buccal side, but no such differences were observed on the lower teeth. The same cement layer was deposited unevenly in different parts of teeth (on its different sides and levels) with a general tendency of increasing in the width of the layer from the top to the lower parts of teeth. As a result of local widening of some cement layers with age, the tooth surface became rough, and knolls and rollers appeared there. As the age increased, external changes in teeth occurred: they became larger, more rounded, and heavier. We described a method for the preliminary determination of the relative age of walruses based on the ratio between the width of cement and dentin on the attrition surface of lower teeth (without cutting).     

Age estimation and growth layer patterns in teeth of crabeater seals: A comparison of techniques

Age estimation of marine mammals provides important information about ecological and life history parameters. Counting growth layer groups (GLGs) in the dentine and cementum of teeth is the most common technique for age estimation in pinnipeds. In this study, we used acid-etched canines (n = 38) and decalcified stained postcanine sections (n = 40) to calibrate readings in mummified crabeater seals (Lobodon carcinophaga). A subsample of this group received a prior cleaning treatment of boiling the teeth with hydrogen peroxide (H₂O₂). Ages ranged from 0 to 31 years. Dentine from canines and cementum from postcanines showed higher estimated ages (maximum 31 years) than dentine from postcanines (maximum 24 years), mainly in those teeth that did not receive prior treatment. Boiling with H₂O₂ has shown to affect cementum structure and, thus, results in underestimated ages, but dentine did not seem to be affected. The results presented here showed that ages can be estimated for the crabeater seal regardless of which tooth/tissue or method is used, at least for seals <13 years old. However, nontreated, stained thin sections of postcanine teeth are recommended because more reliable age estimations in older crabeater seals are obtained.     

Determination of age in the Japanese monkey from growth layers in the dental cementum

The teeth of 14 Japanese monkeys (Macaca fuscata) were examined to establish an exact method of determining age by histological observation of dental cementum. The cementum showed annual growth layers, which were especially remarkable in the incisor root and in the molar cementum deposited at the junction of the roots. The layer of cementum formed in winter appears as a dark layer in stained sections and as a translucent layer in unstained ground sections. In the incisor the first dark and light layers are formed at the age of three years, whereas in the molar they do not appear at a definite age. The layers are thick and clear in the upper medial incisor. As a result, the age of a Japanese monkey can be determined by adding two to the number of dark layers and an outer light layer. It is interesting that the formation of the cementum of the first molar begins a few years after its eruption. The relation between this fact and the pressure of occlusion is discussed.     

The method of age determination of the Pacific walrus (Odobenus rosmarus divergens) using the layered structure of functional teeth

The functional teeth of Pacific walruses that died or were harvested in the Retkyn Spit, Enmelen village, Kolyuchin Island, Vankarem Cape, Enurmino village, and Chegitun River region in 2005, 2007–2008, and 2010–2011 were examined. The definite structure was investigated in animals of their first year of life. The presence of a milk layer in the tooth dentine can be considered as a mark that all the cement layers have been preserved, and the age determination of an individual is precise. The annual increment of dentine significantly changed with age in different parts of the tooth (buccal, lingual, and central), and the annual growth of dentine decreased every year. The growth rate of the upper jaw teeth was significantly higher, and the duration of their growth was much longer than that in the lower jaw teeth. The wearing of dentine and cement layers was unequal in different parts of tooth. Several recommendations for choosing a tooth for the determination of the walrus’s age and for the estimation of age using the layered tooth structure are given.     

Efficiency of wear and decalcification technique for estimating the age of estuarine dolphin <Emphasis Type="Italic">Sotalia guianensis</Emphasis>

Most techniques used for estimating the age of Sotalia guianensis (van Bénéden, 1864) (Cetacea; Delphinidae) are very expensive, and require sophisticated equipment for preparing histological sections of teeth. The objective of this study was to test a more affordable and much simpler method, involving of the manual wear of teeth followed by decalcification and observation under a stereomicroscope. This technique has been employed successfully with larger species of Odontoceti. Twenty-six specimens were selected, and one tooth of each specimen was worn and demineralized for growth layers reading. Growth layers were evidenced in all specimens; however, in 4 of the 26 teeth, not all the layers could be clearly observed. In these teeth, there was a significant decrease of growth layer group thickness, thus hindering the layers count. The juxtaposition of layers hindered the reading of larger numbers of layers by the wear and decalcification technique. Analysis of more than 17 layers in a single tooth proved inconclusive. The method applied here proved to be efficient in estimating the age of Sotalia guianensis individuals younger than 18 years. This method could simplify the study of the age structure of the overall population, and allows the use of the more expensive methodologies to be confined to more specific studies of older specimens. It also enables the classification of the calf, young and adult classes, which is important for general population studies.     

AGE, GROWTH, AND REPRODUCTION IN NEW ZEALAND FUR SEALS

Growth and reproductive biology of New Zealand fur seals ( Arctocephalus forsteri ) were studied by examining 127 seals (57 females, 64 males) killed incidentally in fishing gear in New Zealand waters in 1996. Tooth sections were used to age the animals, and male and female reproductive organs were examined macroscopically and histologically. The maximum age observed was 22 yr for females and 12 yr for males. Males were significantly larger than females, but growth was similar up to 5 yr. Males reached sexual maturity between 5 and 9 yr of age, whereas females did so between 4 and 6 yr. The mean pregnancy rate in females was 0.69 (95% CI = 0.54–0.81).     

Population status and breeding season chronology of Heard Island fur seals

Fur seals were eliminated by sealers at Heard Island soon after its discovery in the 1850s. The first recorded breeding of Antarctic fur seals (Arctocephalus gazella) since sealing was reported in early 1963 (two pups). The most recent survey of the Heard Island fur-seal population was undertaken between November 2000 and March 2001, when 1,012 Antarctic fur-seal pups were born. This represents a fourfold increase since the last complete census in 1987/1988 (13 years), when 248 births were recorded. Pup estimates and counts available for eight breeding seasons since 1962/1963 suggest the population has been increasing at between 12 and 20% per year. Based on pup production, the breeding population is estimated to number approximately 4,100 seals. The number of fur seals on Heard Island peaked in late February/early March at 29,256 indicating that, in addition to the breeding population, a significant number of seals born elsewhere haul out on the island. Most of these are moulting sub-adult and adult males. As in 1987/1988, only one subantarctic fur-seal pup (A. tropicalis) was observed, suggesting this species is not colonising the island, as has been speculated.     

Tooth development in a scincid lizard, Chalcides viridanus (Squamata), with particular attention to enamel formation

Comparative analysis of tooth development in the main vertebrate lineages is needed to determine the various evolutionary routes leading to current dentition in living vertebrates. We have used light, scanning and transmission electron microscopy to study tooth morphology and the main stages of tooth development in the scincid lizard, Chalcides viridanus, viz., from late embryos to 6-year-old specimens of a laboratory-bred colony, and from early initiation stages to complete differentiation and attachment, including resorption and enamel formation. In C. viridanus, all teeth of a jaw have a similar morphology but tooth shape, size and orientation change during ontogeny, with a constant number of tooth positions. Tooth morphology changes from a simple smooth cone in the late embryo to the typical adult aspect of two cusps and several ridges via successive tooth replacement at every position. First-generation teeth are initiated by interaction between the oral epithelium and subjacent mesenchyme. The dental lamina of these teeth directly branches from the basal layer of the oral epithelium. On replacement-tooth initiation, the dental lamina spreads from the enamel organ of the previous tooth. The epithelial cell population, at the dental lamina extremity and near the bone support surface, proliferates and differentiates into the enamel organ, the inner (IDE) and outer dental epithelium being separated by stellate reticulum. IDE differentiates into ameloblasts, which produce enamel matrix components. In the region facing differentiating IDE, mesenchymal cells differentiate into dental papilla and give rise to odontoblasts, which first deposit a layer of predentin matrix. The first elements of the enamel matrix are then synthesised by ameloblasts. Matrix mineralisation starts in the upper region of the tooth (dentin then enamel). Enamel maturation begins once the enamel matrix layer is complete. Concomitantly, dental matrices are deposited towards the base of the dentin cone. Maturation of the enamel matrix progresses from top to base; dentin mineralisation proceeds centripetally from the dentin–enamel junction towards the pulp cavity. Tooth attachment is pleurodont and tooth replacement occurs from the lingual side from which the dentin cone of the functional teeth is resorbed. Resorption starts from a deeper region in adults than in juveniles. Our results lead us to conclude that tooth morphogenesis and differentiation in this lizard are similar to those described for mammalian teeth. However, Tomes processes and enamel prisms are absent.     

Probit and survival analysis of tooth emergence ages in a mixed-longitudinal sample of chimpanzees (Pan troglodytes).

Tooth emergence data from a mixed-longitudinal sample of 58 chimpanzees of known age were analyzed using probit and survival techniques to produce median emergence ages, ranges of variability, and emergence sequences for primary and permanent teeth. Between-group comparisons were made to test for statistically significant differences in emergence ages. No such differences were found between right and left sides, or between maxilla and mandible, for any primary or permanent teeth. Male-female comparisons did demonstrate significant emergence-age differences for some teeth, although they were not always bilaterally symmetrical. More complete data are required to further clarify the nature of sex differences in tooth emergence in chimpanzees. Regression models for age prediction from the number of emerged teeth were generated and indicate that males achieve a given number of emerged teeth at a significantly later age than females. However, when fewer than five teeth have emerged, males are predicted to be younger than females. The sizable root mean square error values for these models suggest that this method of age prediction has limited usefulness owing to the amount of variability in timing of tooth emergence in chimpanzees. The implications of these data for studies on tooth emergence in early hominids are addressed.     

Age,sex, and antemortem loss of teeth in prehistoric Eskimo samples from point hope and Kodiak Island,Alaska

The incidence of teeth lost antemortem was investigated in 244 archeologically derived dried skeletal specimens from the Ipiutak and Tigara burials at Point Hope, Alaska, and 83 Koniag Eskimo specimens excavated at Jones Point, Uyak Bay, Kodiak Island, Alaska. Ipiutak skeletal remains date from approximately 1500 years B.P. and the Tigara remains from 300–400 years B.P. The Kodiak Island sample is undated. Specimens were sexed and aged in five-year groupings using standard techniques. Teeth lost antermortem were identified as having occupied tooth sockets which showed healing of alveolar bone following exfoliation. Numbers of lost teeth were calculated as percentages of total number of tooth sites of each tooth classification for each age, sex, and site subgrouping. Tooth loss was very low in the Kodiak Island sample, with little difference between sexes and no identifiable age trends. The Tigara ramains displayed moderate tooth loss, with strong correlations to increasing age and little differentiation between the sexes. The Ipiutak specimens lost the most teeth antemortem, with notable between-sex differences and strong correlations with increasing age. In all groups loss of anterior teeth was probably due to accident or heavy wear, while loss of posterior teeth was due to heavy wear, periodontal disease, or agenesis.     

A tooth wear scoring scheme for age estimation of the Eurasian lynx (<Emphasis Type="Italic">Lynx lynx</Emphasis>) under field conditions

Within the framework of conservation actions for the Eurasian lynx (Lynx lynx), ageing of individuals is required to assess suitability for translocation and to investigate population dynamics and disease epidemiology. We aimed to develop a standardised ageing tool for free-ranging Eurasian lynx, which would be non-invasive, time- and cost-effective, and applicable under field conditions. We used tooth pictures of 140 free-ranging lynx of known age from Switzerland. Tooth colour, calculus, number of incisor teeth and canine, premolar and molar tooth wear were recorded according to pre-defined criteria. Statistical comparisons among the categories of each criterion revealed significant differences for all criteria. Tooth colour and canine tooth morphology showed obvious and consistent alterations with age. Together with the molar tooth shape, premolar tooth tips, incisor teeth and amount of calculus, they pictured the age-related changes in lynx dentition. Crown fractures, enamel flaking and open pulp cavities were observed with an increasing prevalence over age but were also sporadically seen in juveniles. Based on the obtained results, we developed a classification scheme distinguishing six age classes: <?1 year, 1–2 years, 3–6 years, 7–9 years, 10–13 years, ≥?14 years. The scheme was subsequently tested with the same lynx. Classification success rates of different readers ranged from 69 to 88% but errors did not exceed one age class. The homogenous tooth replacement pattern observed in lynx <?1 year allowed us to develop a separate ageing chart to age juveniles in months. The proposed scheme is a promising tool to objectively assign lynx to meaningful age categories.     

Dental health of elderly confederate veterans: evidence from the Texas State Cemetery

Analysis of the skeletal remains of 50 Confederate veterans provided a unique opportunity to explore the dental health of a geriatric sample. These men, who died between 1907-1932, had an average age at death of 76.7 years. Ninety percent were institutionalized at the Confederate Home for Men (Austin, TX) prior to their deaths. This elderly sample was assessed in terms of caries, antemortem tooth loss (AMTL), abscesses, and linear enamel hypoplasias. On a per tooth basis, the AMTL rate was 57.2%. Of 39 dentate men, 33 (84.6%) had dental caries, and 24.4% (121 of 496) of teeth were carious. Ten (25.0%) of the dentate men had hypoplastic teeth. At least one abscess was seen in 14 (28%) of 50 individuals. Results from this geriatric institutionalized sample are compared to contemporaneous historical samples. Disparities in dental health among these groups may be due to differences in average age at death, and these comparisons allow a better understanding of dental changes that occur with age. The sample is also compared to modern elderly samples: modern groups have higher caries rates, possibly because they retained more teeth. This finding may be due in part to diets in the United States becoming increasingly cariogenic over time. In addition, dental care has moved from the reactive practices seen in the nineteenth and early twentieth centuries (such as tooth extractions) to modern proactive solutions dedicated to preserving and restoring teeth (such as tooth brushing, fluoride treatments, and dental fillings).     

DENSITY DEPENDENCE IN NORTHERN FUR SEALS (CALLORHINUS URSINUS)

This paper summarizes, updates, and interprets information on density-dependent dynamics of populations of the northern fur seal ( Callorhinus ursinus ). Density-dependent changes observed in these populations have involved various aspects of growth (body length, body weight, tooth weight, and size of other skeletal parts, especially the skull), survival, age at maturation, incidence of disease, and time spent foraging. For the population of northern fur seals on St. Paul Island of the Pribilof Islands, which was observed during a major increase and during two significant declines, density-dependent changes that occurred during the growth of the population were reversed during the declines. The Robben Island population in the western Pacific declined after 1965, and the decline was accompanied by changes similar to those observed during the declines on the Pribilof Islands. Although data are not available for all age and sex classes, it appears that most or all components of the populations exhibit similar changes. The overall implication of these changes is that current populations on Robben Island and the Pribilof Islands are reduced to levels below what could be supported by the resources available in their environments. Density dependence for this species is consistent with that of other large mammals, specifically in that vital rates for fur seals ate related to density in a nonlinear fashion.     

Age determination and body growth of the Common duiker Sylvicapra grimmia(Mammalia)

Age determination in the Common duiker Sylvicapra grimmia was investigated by analysis of tooth eruption and replacement sequence, incremental lines of tooth cementum and tooth wear in a unique collection of 48 known-age skulls, and also by analysis by post-natal body growth in known-age duiker. In both the mandible and maxilla, permanent molariform teeth were fully erupted and in wear by 26 months of age. There was little variation in the age of eruption and replacement of all molariform teeth, making this a particularly useful feature of the duiker for age determination purposes. In contrast, the variability in eruption of the incisiforms, coupled with the difficulty in distinguishing deciduous incisiforms from the permanent counterparts, placed an unexpected limitation on the use of these teeth. Although the apparent linear relationship between tooth attrition and age has potential for further investigation as an age determination technique, the cementum annuli were not correlated with chronological age. Theoretical Von Bertalanffy equations were used to analyse body growth with age. It was concluded that because the asymptote of growth was reached at such an early age, and because there is so much individual variation in growth, body growth, including horn growth, is of very limited value for age determination. Female duiker were significantly larger than males.     

Linear enamel hypoplasias as indicators of systemic physiological stress: evidence from two known age-at-death and sex populations from postmedieval London

Enamel hypoplasias are useful indicators of systemic growth disturbances during childhood, and are routinely used to investigate patterns of morbidity and mortality in past populations. This study examined the pattern of linear enamel hypoplasias in two different burial populations from 18th and 19th Century church crypts in London. Linear enamel hypoplasias on the permanent dentitions of individuals from the crypt of Christ Church, Spitalfields, were compared to enamel defects on the teeth of individuals from St. Bride's. The method used involves the identification of enamel defects at a microscopic level, and systemic perturbations are detected by matching hypoplasias among different tooth classes within each individual. The pattern of linear enamel hypoplasias was contrasted between individuals from the burial sites of Spitalfields and St. Bride's, between males and females, and between those aged less than 20 years of age and those aged over 20 years at death. Six different parameters were examined: frequency of linear enamel hypoplasias, interval between defects, duration of hypoplasias, age at first occurrence of hypoplasia, age at last occurrence of hypoplasia, and the percentage of enamel formation time taken up by growth disturbances. All individuals in the study displayed linear enamel hypoplasias, with up to 33% of total visible enamel formation time affected by growth disruptions. Multiple regression analysis indicated a number of significant differences in the pattern of enamel hypoplasias. Individuals from Spitalfields had shorter intervals between defects and greater percentages of enamel formation time affected by growth disturbances than did individuals from St. Bride's. Females had greater numbers of linear enamel hypoplasias, shorter intervals between defects, and greater percentages of enamel formation time affected by growth disturbances than males. There were also differences in the pattern of enamel hypoplasias and age at death in this study. Individuals who died younger in life had an earlier age at first occurrence of enamel hypoplasia than those who survived to an older age. The pattern of enamel hypoplasias detected in this study was influenced by tooth crown geometry and tooth wear such that most defects were found in the midcrown and cervical regions of the teeth, and greater numbers of defects were identified on the anterior teeth. Differences in sensitivity of the parameters used for the detection of enamel hypoplasias were found in this study. The percentage of visible enamel formation time affected by growth disturbances was the parameter that identified the greatest number of significant differences among the subgroups examined.